1. Field of the Invention
The present invention relates to a process for forming a polyester film, and more particularly to a process for forming a polyester film which can obtain a formed body of the polyester film having good slipping property and uniformity in thickness with a good formation ability.
2. Description of the Prior Art
It has been proposed that polyester films can be used as packages by thermoforming them. For example, JP-A-SHO 47-391, JP-A-SHO 51-38335 and JP-A-SHO 62-19090 disclose the thermoforming of non-stretched films made from polyethylene terephthalate (PET), or copolymer or blended polymer of PET. Recently, non-stretched polyester films of PET-system have been in commerce as films called "A-PET" (amorphous PET).
In such proposed polyester films of PET-system for forming, however, in spite of expectance for substituting them for hard polyvinyl chloride sheets, their uses have not been developed so much. The reason is that formation ability thereof is not good and the formed bodies therefrom tend to have relatively great irregularities in thickness.
Moreover, since these polyester films for forming have poor slipping properties, scratches are liable to occur during handling. Further, since they have poor releasing properties from molds in thermoforming, the shapes of the formed bodies therefrom tend to be deformed, and scratches are liable to occur on the surfaces of the formed bodies. Furthermore, since their slipping properties are still poor even in the stage after forming, a decrease in quality occurs in a process after forming. Particularly, when the formed bodies are used as a package and a substance is automatically charged into the respective formed bodies, the formed bodies are stacked and set in a charging machine and they must be smoothly taken out from the machine one by one. When the conventional polyester films for forming are used for such a package and the formed bodies are employed in such a charging system, however, the formed bodies are sometimes caught on some part of the charging machine when they are taken out, and it causes a charging trouble.